I had a Gen IV 454 & the Gen V heads will bolt on but There is a steam passage that has to be drilled into the block for it to work. So it will have to be sent out to a machine shop.
The coolant passages on the decks of Gen V blocks are larger & of a different shape than those used in Mark IVs. This prevents installing production Mark Iv heads without a conversion kit. Some aftermarket heads can be used on either Mark IV or GenV blocks.
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1977 Trans Am 400CI R/A IV.
**Looks can be deceiving**
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